Method of electroplating to produce fissure network chromium plating



T. H. WEBERSINN ET AL 2,430,750

METHOD OF ELECTRUPLATING TO PRODUCE FISSURE NET-WORK CHROMIUM PLATINGFiled July 18, 1944 INVHVTOR. Holman: nmmsmu JACOB HYNI-R Patented Nov.11, 1947 METHOD OF ELECTROPLATING TO PRO- DUCE FIS SURE PLATING NETWORKCHROMIUM Theodore H. Webersinn and Jacob Hyner, Waterbury, Conn.,assignors to United Chromium, Incorporated, New York, N. Y., acorporation of Delaware Application July 18, 1944, Serial No. 545,506

4 Claims. (Cl. 204-35) This invention relates to methods of electrodepositing chromium in which the conditions of deposition are socorrelated and controlled as to give a chromium plate which ispredisposed to the formation of fissure net-works and which upon etchinggive mud-crack type surfaces having plateau areas which do not exceed adesired size; sa d surfaces being particularly suited after mechanicalfinishing to frictional contact with other surfaces.

It is desirable in some applications of chromium to parts subject tofrictional wearing-effects to avoid any tendency of the contacting partsto seize, scuff, or score, especially in apparatus working under-heavyloads at high speeds, such as rotary seals, compressors, internalcombustion engines, etc. It has heretofore been proposed to pit orindent the surface of chromium electrodeposits to avoid such tendency toseize, scuff or score.

We have discovered that by using the usual commercial current densitiesand anysuitable chemical or electrochemical method of etching, mud-crackproducing types of chromium plate are obtained by correlatingcomposition of the chromium plating bath with temperature of the bathand maintaining these correlated conditions during the platingoperations.

The accompanying drawing is a graph showing the correlations of bathcomposition ratios, temperatures, and average sizes of fissure networkafter etching under conditions hereinafter specified.

The compositions of our chromium plating baths should be maintained sothat the ratios of grams per liter of chromic acid (CI'O3) to grams perliter of total catalyst acid radicals expressed as sulphate (S04) arefrom 50 over 1 to 150 over 1. Thick electrodeposits of chromium on theorder of three to fifteen thousandths of an inch are ordinarily used. Toproduce chromium electrodeposits predisposed to the formation of fissurenet-works and which upon etching give mudcrack type chromium surfaces,bath temperatures from about 120 F. (49 C.) to 160 F. (71 C.) with bathshaving the aforementioned ratios have been used. In practice, a bathtemperature within said limits is selected and maintained.

Suitable cathode current densities for bath temperatures from 120 F. to160 F. are in the range 1 to 12 amperes per square inch, the highercurrent densities being used at the higher temperatures. Lower andhigher current densities 2 lower. and with higher current densitiesthere is the likelihood of treeing.

Compared with a bath maintained at a chromic acid-catalyst acid radicalratio of over 1, temperature and current density being the same,

a bath maintained at a higher ratio, over 1 for example, will produce achromium electrodeposit predisposed to the production, upon etchingunder the same conditions within limits hereinafter set forth, ofmud-crack type chromium surfaces of larger plateau size than the first.Conversely baths maintained at a ratio less than 100 over 1, all otherconditions remaining the same, will result in smaller plateau sizes.

For baths having low ratios, there is a minimum temperature within therange 120 F. to 160 F. below which mud-crack type chromium surfacescapable of being mechanically finished to produce average plateau sizesof the order of /64" diameter cannot be practically obtained. Thus, fora bath having a ratio of 100 over 1, for example, operated attemperatures substantially below F., mud-crack type chromium surfacescapable of being mechanically finished to produce average plateau sizesof the order of l/s4" diameter will not be produced. Moreover, when sucha bath is operated at temperatures higher than 130 F., but below 160 F.,mud-crack type chromium deposits will be produced having plateau areaswhich increase in size as the temperature increases. For baths havingratios higher than 100 over 1 but less than over 1 temperatures lowerthan 130 F. can be used to obtain satisfactory mud-crack type chromiumsurfaces. With the lower ratios, the higher temperatures are preferred,and for the lower temperatures the higher ratios are preferred; with thehigher ratios, both the lower and higher temperatures may be used, butfor a particular size of plateau, they must be correlated keeping allother conditions constant. For a given temperature, the plateau sizeincreases with the increase in ratio, and for a given ratio, the plateausize increases with increase in temperature. Change in temperature has agreater relative effect on change in size of plateau than change inratio.

The etching to develop the net-Works of fissures in the predisposedchromium electrodeposit may be done in any suitable manner. It may bedone electrochemically, with the article connected as the cathode, orchemicall and electrochemically combined, or chemically, as discoveredby Webersinn (set forth in application Sr. No. 510,210) or anodically,or otherwise.

The formation of the net-works of fissures may be carried outelectrolytically by immersing the chromium deposit as a cathode in asuitable solution. Solutions of oxalic acid, sulphuric and chromicacids, sulphuric acid, phosphoric acid, hydrochloric acid, citric acid,ferric sulphate, are examples of those which have been used. Many otherelectrolytic solutions of acids and salts which have a low pH may beused. Warm or hot solutions are used, the activity thereof increasingwith increase of temperature. Concentration of these solutions alsoaffects their activity. With the article having the predisposed chromiumelectrodeposit thereon, immersed in the electrolytic solution, andconnected as a cathode, a current of proper density is passed for thenecessary length of time to give the desired plateau size and fissuredepth. Very high current densities may prevent the formation of thenet-works of fissures; current densities of A to 3 amperes per squareinch are generally satisfactory for cathodic etching. Short time etchingresults in shallow fissures; prolonged etching results in excessiveremoval of chromium and subdivision of plateaus which on subsequentmechanical finishing tend to crumble.

The formation of the net-works of fissures may be carried outelectrolytically and chemically in combination, whereby the chromiumelectrodeposit is acted on while it is cathodic during the passage of anelectric current of proper density for a few minutes in a suitableelectrolyte, after which the treatment is continued by chemical actionin the same or another bath without current. This may be carried out ina succession of cycles if desired. After the chromium has been activatedby the cathodic action which takes place during the passage of thecurrent, evolution of hydrogen continues after the current has beenstopped. The electrolytic solution may be one of those described above.The degree of etching has a similar effect to that described above.

The formation of the net-work of fissures may be carried out chemicallyby immersing th chromium electrodeposit in a solution which attackschromium. Examples of such solutions are hydrochloric acid or warmsulphuric acid. In many cases the chromium electrodeposit must beactivated before the attack begins; this activation may be convenientlyaccomplished by electrolyzing the chromium cathodically. Withactivation, solutions such as described above for electrolytic etchingcan be used for chemical etching, and the degree of etching has asimilar effect to that described above.

The progress of the formation of the fissure net-work in the course ofetching can be observed visually, by removing the article from time totime and examining it.

It is a characteristic of the predisposed chromium electrodepositsproduced in accordance with this invention that, when subjected toetching of the character described herein, the attack thereon occurs atlines in the electrodeposit, and is largely confined to lines providedthe etching is not too prolonged, thus developing fissure net-works of anature which giv mud-crack type chromium surfaces which retain theirmud-crack type characteristics after mechanical finishing.

Fissure net-works having deep and narrow fissures with relatively largesize plateaus are advantageous since there is less crumbling of the\chromium in subsequent mechanical finishing operations, less of thechromium need be removed in these mechanical finishing operations toobtain the desired smoothness on the surface of the plateaus, and fromthis it follows that to obtain the same thickness of chromium with amudcrack type surface on a finished article less chromium need bedeposited than where the nature of the fissure net-works is such as torequire considerable removal of chromium in the mechani-' cal finishingoperation to obtain the desired smoothness of the surface.

On cylinder bores of high output internal combustion engines, it hasbeen found that a mudcrack type chromium surface having plateausone-sixty-fourth to one-thirty-second of an inch in diameter areespecially advantageous. The

present invention enables mud-crack type chromium surfaces with plateausof such size, and of other sizes, to be readily and reproduciblyobtained, in conjunction with suitable etching treatments, such forexample as those described in the aforesaid Webersinn application.

Specific examples of practices in which the present invention isutilized follow:

Cathodic treatment (for 15 min.)

amps. per. sq. in .5

Result Mud-crack type surface with average plateau size approximatelydiameter.

EXAMPLE II Chromium electrodeposttion Bath and plating conditions exceptratio 1.

same as Example I,

Etching Same as Example I.

Result Mud-crack type surface with average plateau size approximately 5diameter.

EXAMPLE III Chromium electrodeposition Bath and plating same as Example1, except ratio /1.

Etching Same as Example I.

Result Mud-crack type surface with average plateau size approximately &diameter.

EXAMPLE IV Chromium electmdeposition Bath: Same as Example I (ratio100/1).

Mud-crack surface with average plateau size approximately EXAMPLE VChromium electrodeposition Bath: Same as Example I, except ratio 75/ 1.

Temperature F 155 Current density amps. per.sq. in 4.5

Etching Same as Example I.

Result Mud-crack type surface with average plateau size approximately ,6diameter.

The chromium electrodeposits were in each example from five to sixthousandths of an inch thick.

The correlation between chromic acid-catalyst acid radical ratio,temperature of the plating bath and average plateau size to be producedin the chromium electrodeposit for the degree of etching given above, isshown by the accompanying graph. For example, if it be desired to obtaina one-sixty-fourth of an inch average diameter of plateau, the ordinateextending from the onesixty-fourth mark on the horizontal line of thegraph (axis of abscissas) intersects all five ratio curves, and thetemperature for each ratio found by the abscissa which extends to thevertical line on the graph (axis of ordinates) from the points ofintersection of the ordinate at the onesixty-fourth mark with each ofthe ratio curves. The abscissas from each of these points ofintersection give the temperatures as follows: ratio 75 over 1,approximately 156 F.; ratio 100 over 1 approximately 143 F.; ratio 115over 1, approxie mately 137 F.; ratio 125 over 1, approximately 132 F.;and ratio 150 over 1, approximately 127 F. With this knowledge as aguide the plater is enabled to base his choice of a correlated ratio andtemperature of plating bath and a degree of etching equivalent to thatgiven above for a given average plateau size.

This application is a continuation in part of our application No.510,970, filed November 19, 1943.

What is claimed is:

1. A method of producing articles having chromium electrodepositsthereon with a fissure network therein and firm plateau areas withinsaid fissure net-work having a minimum average diameter of eightthousandths of an inch, for sustaining the frictional load of movingparts bearing on said plateaus, comprising electrodepositing thechromium from a chromic acid bath to a minimum thickness of onethousandth of an inch, at the usual commercial current densities for thebath temperature at which the plating is done, within the range 1 to 12amperes per square inch, under correlated conditions of temperature andratio of Cr03 to S04 related'to a particular average diameter plateau,within a temperature range of 120 F. and 160 F, and a Cr03 to S04 ratiorange of 75 to 1 and 150 to 1, etching the chromium. electrodeposited opa fissure net-work with plateaus therein or a particular averagediameter, ranging from eight thousandths of an inch upward, to whichsaid chromium electrodeposit is predisposed by the correlatedtemperature and Cr03 to S04 ratio at which it is electrodeposited, andmechanically finishing the firm plateaus to produce a smooth bearingsurface with said'fissure net-work remaining therein, the correlatedconditions of temperature and CrOa to S04 ratio for electrodecositingthe chromium being further defined as follows: ClOx to S04 ratio 75120 1and temperature 148 F. for plateaus of eight thousandths of an inchaverage diameter, and progressively higher temperatures at said to 1ratio for progressively larger average diameter plateaus; CrOs to S04ratio .100 to 1 and temperature 132 F. for plateaus of eight thousandthsof an inch average diameter, and progressively higher temperatures atsaid to 1 ratio for progressively larger average diameter plateaus; CiOato S04 ratio to 1 and temperature 129 F. for plateaus of eightthousandths of an inch average diameter, and

progressively higher temperatures at said 115 to 1 ratio forprogressively larger average diameter plateaus; CIO: to S04 ratio to 1and temperature 126 F. for plateaus of eight thousandths of an inchaverage diameter, and progressively higher temperatures at said 125 to 1ratio for progressively larger average diameter plateaus; CrO: to S04ratio to 1 and temperature 123 F. for plateaus of eight thousandths ofan inch average diameter, and progressively higher temperatures at said150 to 1 ratio for progressively larger average diameter plateaus; andCrOs to S04 ratio values intermediate to those stated above beingcorrelated to temperature values intermediate to those which correspondto the stated ratio values.

2. A method of producing articles according to claim 1, wherein thefissure net-work produced by the etching is of the character obtained byetching the aforesaid chromium electrodeposit in an etching solutionconsistin of 290 g./l. phosphoric'acid, l0 g./l. potassium dichromateand 2 g./l. trivalent chromium added as potassium chrome alum at atemperature of F., in which solution the chromium electrodeposit isconnected as a cathode and current passed thereto for 15 minutes at acathode current density of one-half ampere per square inch.

3. A method of producing articles having chromium electrodepositsthereon with a fissure network therein and firm areas within saidfissure net-work having an average diameter of two hundredths of an inchfor sustaining the frictional load of moving parts bearing on saidplateaus, comprising electrodepositing the chromium from a chromic acidbath to a minimum thickness of one thousandth of an inch at the usualcommercial current densities for the bath temperature at which theplating is done, within the range 1 to 12 amperes per square inch, undercorrelated conditions of temperature and ratio of CrOa to $04 related tosaid average plateau diameter, etching the chromium electrodeposited asherein stated to develop a fissure net-work with plateaus therein ofsaid average diameter of two hundredths of an inch to which itispredisposed, and mechanically finishing the firm plateaus to produce asmooth bearing surface with said fissure net-Work remaining therein, thecorrelated conditions of temperature and C103 to S04 ratio forelectrodepositing the chromium being defined in the following table, thevalues of temperature and ratio interas herein stated to devel-- 7mediate to those tabulated being obtained by interpolation;

Ratio :0. to 904 fi fi" to 1--- 151 109 f0 1.-. 146 to 1.. 149 to 1...136 150 to 1..

4. A method of producing articles according to claim 3 wherein saidcorrelated CrOa to S04 ratio and temperature values are between 100 to 1and 125 to 1 ratios and approximately 146 F. and 136 F. temperatures.

THEODORE H. WEBERSINN. JACOB HYNER.

REFERENCES CITED The following references are of record in the file ofthis patent:

OTHER REFERENCES Transactions of the Electrochemical Society, vol. 53(1928), Grant, pages 509-519.

Transactions of the Electrochemical Society,

vol. 54 (1928) Baker et 9.1., pages 337-345. 15 Transactions of theElectrochemical Society,

vol. 80 (1941) Dubpernell, page 289.

Transactions of the Electrochemical Society, vol. 80 (1941),Dubperne1l,page 595.

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